1. Field of the Invention
The invention relates to a filling level sensor for a liquid container such as a fuel tank in a motor vehicle having a lever arm which supports a float and whose pivot movement is converted into an electrical output signal corresponding to the filling level of the liquid in the container.
2. Description of the Related Art
Lever-type fill level transmitters having a lever arm with a float fixed thereto are often used in fuel tanks and are known. The known lever-type transmitters are typically fixed to a structural part in the fuel tank, e.g. a conveying unit. The known lever-type transmitter further comprises a support part on which a ceramic with a thick-film resistor network is arranged. A sliding-action contact connected to the lever arm sweeps over the resistor network to generate an electrical signal corresponding to the filling level dependent on the pivot movement. The disadvantage of these lever-type transmitters is that the resistor network is arranged in the fuel and, consequently, has to be resistant to said fuel. Furthermore, the sliding-action contact is subject to wear. Moreover, these known lever-type transmitters do not have diagnosis capability. That is, changes in the measured values caused by deposits or similar effects cannot be identified. Accordingly, these changes in measured values over time cause the output signal to deviate so that it no longer corresponds to the actual filling level.
To avoid corrosion and wear on the sensor of the lever-type transmitter, it is known to use sensors which operate contactlessly such as, for example, reed contacts for filling level measurement. In a fill level transmitter having reed contacts, one or more reed contacts are arranged as part of an evaluation circuit in the liquid container and a float bearing a magnet is arranged in a movable manner along the reed contacts. The reed contact located proximate to the float is closed via the magnetic field of the magnet. A corresponding electrical signal is obtained by the evaluation circuit at this reed contact which corresponds to the respective filling level. A problem with filling level sensors of this type is that they require a complicated configuration because plural sensors must be arranged in a distributed manner over the entire height of the liquid container. The arrangement of plural sensors requires a relatively large volume which has a negative effect on the remaining useful volume of the container.
An object of the present invention is to provide a filling level sensor for a liquid container which is constructed in a simple manner and in which the sensor does not contact the medium. Furthermore, the object of the present invention is to provide a filling level sensor for a liquid container in which the filling level sensor is mounted in a simple manner and is mountable in any desired position.
The object is achieved by a filling level sensor for a liquid container comprising a support part, a lever arm having a first end and a second end, wherein the second end is pivotally mounted on the support part, a float arranged at the first end of the lever arm such that the lever arm is pivotally deflectable in response to a change in a filling level in the liquid container, a magnetic sensor having an output signal corresponding to the filling level in the liquid container, and a magnetic device having a magnetic field acting on the magnetic sensor and operatively arranged for moving in response to a pivotal deflection of the lever arm, wherein the magnetic field acting on the magnetic sensor changes during the pivotal deflection of the lever arm and thereby changes the output signal.
According to the present invention, a filling level sensor has a magnetic device with at least one contactless magnetic sensor. A lever arm connected to a float is operatively connected to the magnetic device. The pivotal deflection of the lever arm moves the magnetic device relative to the magnetic sensor so that the magnetic field acting on the magnetic sensor changes in response to the relative movement of the magnetic device. This change in the magnetic field causes a change in the output signal of the magnetic sensor which corresponds to the change in filling level.
The magnetic sensor of this filling level sensor may be encapsulated so that it does not contact the medium in the liquid container. The encapsulation of the magnetic sensor simplifies the detection of the filling level by the lever arm and float and makes the detection cost-effective. As a result, this filling level sensor is particularly suitable for use in measuring the fill level of aggressive media such as fuel for internal combustion engines. A support part in which the lever arm is mounted may be used to fix the filling level sensor to built-in components in the liquid container. However, the filling level sensor may also be inserted into an opening in the liquid container and connected to the container via a flange on the support part. In this arrangement, the magnetic sensor is arranged in the flange. Furthermore, the magnetic sensor may be ventilated so that the magnetic sensor is not attacked even by permeating media in the liquid container.
In a further embodiment, the magnetic device comprises a cam disk connected to the lever arm and composed of a magnetic material. Liquid containers comprising fuel tanks for motor vehicles are typically formed in a complicated manner such that the relationship between filling level and filling quantity in the container is nonlinear. According to the present invention, the pivot movement of the lever arm may be converted into a magnetic sensor output signal corresponding to the filling level liquid containers with a nonlinear tank characteristic if the cam disk is designed in accordance with the tank characteristic. The conversion of the pivot movement of the lever arm by means of a cam disk allows the filling level sensor to be arranged at any desired location in the liquid container. Accordingly, an exclusively upright arrangement of the filling level sensor is not necessary.
Furthermore, the cam disk may further comprise partly magnetized regions or regions having different magnetic polarities so that not only the change in strength but also the change in position of the magnetic field acting on the magnetic sensor produces a magnetic sensor output signal which corresponds to the instantaneous filling level in the liquid container.
In yet another embodiment, the magnetic device includes a magnet movably arranged therein and brought to bear on an end of the cam disk so that a corresponding movement of the cam disk causes the magnet to move linearly with respect to the magnetic sensor. The advantage of this embodiment is that the cam disk may be composed of a plastic, for example, instead of a magnetic material.
To ensure permanent contact between the magnet and the cam disk, the magnet may be brought to bear against the cam disk by the urgency of a spring. This allows the magnet to be arranged in a configuration other than exclusively upright on the cam disk.
In a further embodiment, a plunger is arranged between the magnet and the cam disk. The plunger allows the lever arm and the magnetic sensor to be decoupled spatially, so that the magnetic sensor is arranged in the container wall by means of the flange while the lever arm is arranged with the float at a suitable location in the liquid container.
In a further refined embodiment, the filling level sensor is inserted into an opening in the side wall of the liquid container. In the case of fuel tanks of motor vehicles, this arrangement allows easier accessibility for repair and maintenance work and can be reached without demounting the fuel tank.
By way of example, passive magnetic position sensors, of the kind disclosed in German reference DE 196 48 539 A1, may be used as the contactless magnetic sensor. Furthermore, Hall elements, reed contacts or similar sensors may alternatively be used. These sensors have the advantage that they have a diagnosis capability. By way of example, reference points may be interrogated and/or adjusted by a corresponding electronic unit.